One known method of increasing the moldability of a polytetrafluoroethylene and the creep resistance and transparency of a molded product thereof is copolymerizing tetrafluoroethylene and a minute amount of comonomers. Such a polytetrafluoroethylene modified by copolymerization with a minute amount of comonomers is used as a coating material for wires and coaxial cables because it has better moldability and processability than a tetrafluoroethylene homopolymer and has excellent electrical properties.
Patent Document 1 teaches as a modified polytetrafluoroethylene a fine powder which is a modified polytetrafluoroethylene fine powder containing copolymerized tetrafluoroethylene, perfluoro(n-butyl)ethylene, and perfluoro(propyl vinyl ether) or hexafluoropropylene, the fine powder having a melt viscosity of 1×108 Pa·s.
Also, Patent Document 2 teaches a method of manufacturing modified polytetrafluoroethylene fine powder by a polymerization reaction comprising copolymerizing tetrafluorethylene (TFE) with perfluorobutyl ethylene and hexafluoropropylene (HFP) in an aqueous medium in the presence of a fluorine-containing dispersing agent at a temperature in the range of 10-90° C. and under an average pressure in the range of 6-30 kg/cm2G, the copolymerizing being carried out by feeding the TFE to the aqueous medium, feeding the perfluorobutyl ethylene to the aqueous medium in the early stage of the polymerization reaction, feeding the HFP to the aqueous medium after at least 75% of the tetrafluoroethylene to be copolymerized has been consumed in the polymerization reaction, and after completing the polymerization reaction, coagulating the resultant primary grains of modified polytetrafluoroethylene (modified PTFE) and drying the resultant coagulum to obtain the modified PTFE powder, the feeding of the perfluorobutyl ethylene and the HFP being carried out so that the polytetrafluoroethylene powder contains 0.01-0.07 wt % of the perfluorobutyl ethylene and 0.01-0.05 wt % of the HFP, the total amount of the perfluorobutyl ethylene and the HFP present in the polytetrafluoroethylene powder being 0.03-0.08 wt %, based on the weight of TFE in the powder, the average grain size of the primary grains being in the range of 0.1-0.5 μm, the spheroidicity of the primary grains being 1.5 or lower, and the thermal degradation index of the powder being 20 or lower.    Patent Document 1: JP 3764752 B    Patent Document 2: JP 3616784 B